• Plasma contains 3 main classes of proteins: albumin, globulin, and fibrinogen; whereas serum only contains albumin and globulin (without fibrinogen-containing blood clots).
Albumin: synthesized by the liver, carries vital compounds (e.g. fatty acids, Ca, hormones, bilirubin) and maintains osmotic pressure in the blood.
Globulin: consists of α1, α2, β, and γ globulins, mostly synthesized by the liver, except for γ globulins (also known as immunoglobulins) made by lymphocytes.
Fibrinogen: also synthesized by the liver, plays a major role in blood clotting.
• Serum total protein and albumin levels are routinely measured as part of the comprehensive metabolic panel (CMP), and serum globulin level can be calculated by substracting albumin from total protein level.
• Since albumin makes up the majority (60%) of plasma proteins, hypoproteinemia often occurs concurrently with hypoalbuminemia, which is the result of either a decrease in protein/ albumin synthesis by a diseased liver, or a loss of protein into the interstitial space, GI tract, kidney tubules, or skin.
• On the other hand, hyperproteinemia might suggest hemoconcentration due to dehydration or globulin overproduction (often γ-globulin such as in the case of hypergammaglobulinemia).
• When albumin and globulin levels trend in opposite directions, a normal total protein level might be seen. In these cases, taking the albumin to globulin ratios would be helpful in diagnosing the underlying etiologies.
A low albumin/globulin ratio suggests either hypoalbuminemia and/or hyperglobulinemia, seen in malignancy (hematologic and solid tumors), chronic inflammation (autoimmune disorders, chronic infection), or chronic liver dsease.
A high albumin/globulin ratio suggests hypoglobulinemia, often seen in immunodeficiency disorders.
